Add D2Q9 MRT from literature

lbmpy/methods/creationfunctions.py

@@ -432,7 +432,16 @@ def mrt_orthogonal_modes_literature(stencil, is_weighted, is_cumulant):
     x, y, z = MOMENT_SYMBOLS
     one = sp.Rational(1, 1)
 
-    if have_same_entries(stencil, get_stencil("D3Q15")) and is_weighted:
+    if have_same_entries(stencil, get_stencil("D2Q9")) and is_weighted:
+        # Reference:
+        # Duenweg, B., Schiller, U. D., & Ladd, A. J. (2007). Statistical mechanics of the fluctuating
+        # lattice Boltzmann equation. Physical Review E, 76(3)
+        sq = x ** 2 + y ** 2
+        all_moments = [one, x, y, 3 * sq - 2, 2 * x ** 2 - sq, x * y,
+                       (3 * sq - 4) * x, (3 * sq - 4) * y, 9 * sq ** 2 - 15 * sq + 2]
+        nested_moments = list(sort_moments_into_groups_of_same_order(all_moments).values())
+        return nested_moments
+    elif have_same_entries(stencil, get_stencil("D3Q15")) and is_weighted:
         sq = x ** 2 + y ** 2 + z ** 2
         nested_moments = [
             [one, x, y, z],  # [0, 3, 5, 7]

lbmpy/moments.py

@@ -282,7 +282,7 @@ def is_bulk_moment(moment, dim):
     for prefactor, monomial in moment:
         if sum(monomial) == 2:
             quadratic = True
-            for i, exponent in enumerate(monomial):
+            for i, exponent in enumerate(monomial[:dim]):
                 if exponent == 2:
                     found[i] += prefactor
         elif sum(monomial) > 2:

lbmpy_tests/test_momentbased_methods_equilibrium.py

@@ -70,19 +70,12 @@ def test_relaxation_rate_setter():
 
 
 def test_mrt_orthogonal():
-    m = create_mrt_orthogonal(get_stencil("D2Q9"), maxwellian_moments=True, weighted=False)
-    assert m.is_orthogonal
-
-    m = create_mrt_orthogonal(get_stencil("D2Q9"), maxwellian_moments=True, weighted=True)
-    assert m.is_weighted_orthogonal
-
-    m = create_mrt_orthogonal(get_stencil("D3Q19"), maxwellian_moments=True, weighted=False)
-    assert m.is_orthogonal
+    m_ref = {}
 
-    m = create_mrt_orthogonal(get_stencil("D3Q19"), maxwellian_moments=True, weighted=True)
+    moments = mrt_orthogonal_modes_literature(get_stencil("D2Q9"), True, False)
+    m = create_mrt_orthogonal(get_stencil("D2Q9"), maxwellian_moments=True, nested_moments=moments)
     assert m.is_weighted_orthogonal
-
-    m_ref = {}
+    m_ref[("D2Q9", True)] = m
 
     moments = mrt_orthogonal_modes_literature(get_stencil("D3Q15"), True, False)
     m = create_mrt_orthogonal(get_stencil("D3Q15"), maxwellian_moments=True, nested_moments=moments)
@@ -102,6 +95,10 @@ def test_mrt_orthogonal():
     for weighted in [True, False]:
         for stencil in ["D2Q9", "D3Q15", "D3Q19", "D3Q27"]:
             m = create_mrt_orthogonal(get_stencil(stencil), maxwellian_moments=True, weighted=weighted)
+            if weighted:
+                assert m.is_weighted_orthogonal
+            else:
+                assert m.is_orthogonal
             bulk_moments = set([mom for mom in m.moments if is_bulk_moment(mom, m.dim)])
             shear_moments = set([mom for mom in m.moments if is_shear_moment(mom, m.dim)])
             assert len(bulk_moments) == 1